A method for controlling in closed loop the torque of one or more electric motors of an electric powertrain of a vehicle

Abstract

There is described a method for controlling in closed loop a torque of one or more electric motors (M1; M2; M3; M4 ) of an electric powertrain of a vehicle (V). The method determines corrections to be applied to torque values determined in open loop, wherein the corrections are distributed according to a target torque distribution ratio.

Description

[0001] "A method for controlling in closed loop the torque of one or more electric motors of an electric powertrain of a vehicle"

[0002] ★★★★

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention relates to vehicles with an electric powertrain of the type including one or more traction motors distributed between a front axle and a rear axle.

[0006] Prior Art

[0007] In the vehicles with an electric powertrain it is of paramount importance to control the power delivery from the battery or the batteries to the electric motor (s) (and vice versa, in the regeneration mode) so as to respect the constraints of torque delivery and distribution envisaged for the vehicle dynamics targets, and so as to avoid load profiles (for the motors and for the batteries) which may damage the motors and / or the batteries .

[0008] However, in the prior art the delivery of electric power to the motors, as well as the power supply to the batteries in the regeneration mode, are only controlled based on the torque targets envisaged by the vehicle dynamics. In other words, operating conditions are accepted which - albeit temporarily - exceed power delivery or supply thresholds having a critical nature. Moreover, exceeding said thresholds often takes place without being noticed by the control strategy of the powertrain, precisely because the latter is only based on torque targets for each motor, and therefore it is intrinsically ineffective as regards the implementation of a corrective action of any kind for controlling (and moderating) and electric power flow.

[0009] As a partial solution of the technical problem in question, it is possible to implement methods for controlling the torque of the electric motors which are purely based on models, i.e. wherein the control is operated in open loop. An example of said methods has been proposed by the Applicant in the Italian Industrial Invention Patent Application n. 102023000023517. Albeit being effective in a wide range of operating conditions, these methods are intrinsically unable to take into account further influencing factors which appear suddenly and are not envisaged (or cannot be envisaged) by the calculation model in open loop, nor is it possible, consequently, to implement corrections based on said further factors.

[0010] Object of the Invention

[0011] The invention aims at solving the technical problems outlined in the foregoing. Specifically, the object of the invention consists in providing a method for controlling, particularly for controlling in real time, one or more electric motors of the electric powertrain of a vehicle, while respecting both torque distribution targets within the powertrain, which are determined based on the dynamics needs of the vehicle, and threshold values of power delivery or absorption, as well as also taking into account further influencing factors which appear suddenly and are not contemplated (and cannot be contemplated) by a calculation model in open loop, wherein it is consequently impossible to implement corrections based on said further factors.

[0012] Summary of the Invention

[0013] The object of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention.

[0014] Brief Description of the Figures

[0015] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only and wherein:

[0016] - Figure 1 is a block diagram representative of a method according to the invention,

[0017] - Figure 1A shows a general diagram of a vehicle whereon it is possible to implement the method according to the invention, whereas Figure IB shows a preferred embodiment thereof;

[0018] - Figure 2 shows a first sequence of deductions of the method according to the invention, and Figures 3 and 4 show a practical implementation thereof,

[0019] - Figure 5 shows a second sequence of deductions of the method according to the invention, and Figures 6 and 7 show a practical implementation thereof.

[0020] Detailed Description

[0021] In various embodiments, referring to Figure 1 and Figure 1A, the present invention comprises a method for controlling a torque of one or more electric motors Ml; M2; M3; M4 of an electric powertrain of a vehicle V. The method is described with reference to a very general configuration of a powertrain, comprising a first electric motor Ml associated with a left wheel RL of a rear axle RA, a second electric motor M2 associated with a right wheel RR of the rear axle RA, a third electric motor M3 associated with a left wheel FL of a front axle FA, and a fourth electric motor M4 associated with a right wheel FR of the front axle FA, but it is generally applicable to a plurality of configurations having a smaller number of motors and a different arrangement and association thereof, such as e.g. a preferred configuration (Figure IB) which has the motors Ml and M2 associated with the wheels RL and RR, respectively, and the third electric motor M3 associated with both wheels FL and FR of the front axle FA. According to the invention, and referring to Figure l, wherein the method is schematically shown by means of a block diagram having the general reference 1, the method comprises:

[0022] - defining, for each n-th electric motor Ml, M2, M3, M4 (n = 1, 2, 3, 4), a first reference limit value Piim,n,proPof an n-th electric power flow absorbed by the n-th electric motor, and defining, for each n-th electric motor Ml; M2; M3; M4, a second reference limit value Piim,n,reg of an n-th electric power flow generated by the n-th electric motor,

[0023] - defining a first overall reference limit value Piim,ioi PROP of the absorbed electric power flow, comprising a sum of each n-th limit delivered power flow Piim,n,prop, and define a second overall reference limit value Piim,TOTREG of the generated electric power flow, comprising a sum of each n-th limit generated power flow Plim,n,reg!

[0024] - defining (block OL) a first extreme reference value TnfPROpOL for the torque Tndelivered by each n-th electric motor as a function of said first overall limit value Piim,TOT PROP of the absorbed electric power flow and of a boundary condition formulated as a function of the torque Tnof one or more of the electric motors (blocks m, TV), and defining a second extreme reference value Tn,REG OL for the torque Tnabsorbed by each n-th electric motor as a function of said second overall limit value Piim,TOTREG of the generated electric power flow and of a boundary condition formulated as a function of the torque Tnof one or more of the electric motors (blocks m, TV),

[0025] - determining (block CL) a first torque correction TPROP CL to be applied to the one or more first reference extreme values Tn,pRopOL of the torque Tndelivered by each n-th electric motor, and calculating a second torque correction TREG CL to be applied to the one or more second extreme reference values Tn,REG OL of the torque Tnabsorbed by each n-th electric motor,

[0026] - splitting (block mCL) the first torque correction TCL,PROP into a first correction fraction T3,RROP_CL; T4,RROP_CL associated with the front axle FA of the vehicle, and into a second correction fraction TifRROpCL; T2,RROP CL associated with a rear axle RA of the vehicle as a function of a target torque split ratio m, and splitting said second torque correction TCL,REG into a third correction fraction T3fREG CL; T4fREG CL associated with the front axle FA of the vehicle and into a fourth correction fraction T4fREG CL; T2,REG CL associated with the rear axle RA of the vehicle as a function of the target torque split ratio m,

[0027] - applying the first correction fraction T3fRROpCL; T4,PROP CL to the set of first extreme reference values of the torque delivered to the front axle by one or more corresponding electric motors,

[0028] - applying the second correction fraction TifRROpCL; T2,PROP CL to the set of the first extreme reference values of the torque delivered to the rear axle by one or more corresponding electric motors,

[0029] - applying the third correction fraction T3fREG CL; T4,REG CL to the set of the second extreme reference values of the torque absorbed from the front axle by one or more corresponding electric motors, and

[0030] - applying the fourth correction fraction T4fREG CL; T2,REG CL to the set of the second extreme reference values of the torque absorbed from the rear axle by one or more corresponding electric motors.

[0031] The method steps listed in the foregoing will now be described in detail.

[0032] As regards the definition of the values Piim,n,prop and Piim,n,reg, in preferred embodiments - including the one shown in the diagram of Figure 1 - said values are calculated according to the fashion described in the document 102023000023517 mentioned in the foregoing. In order to recall the relevant content of said document, in the presence of one or more electric motors operatively associated with a front axle and / or to a rear axle of the vehicle, or with respective single wheels of one and the same axle, a power flow is exchanged between each motor and (at least) an axle or (at least) a wheel of the vehicle, for the traction of the latter. The phrase "power flow" designates both a power flow into the electric motor (from a battery BT), i.e. a flow which originates a driving action by the motor, with power being delivered by the motor, and a power flow out of the electric motor (and into the battery BT), i.e. a flow which originates when the electric motor is subjected to a resistant load (braking or slowing down due to the vehicle inertia) and absorbs power while operating as an electric generator.

[0033] In each limit value of the n-th power flow Piim,n,prop and Piim,n,reg, the index n = 1, 2, 3, 4 in the presently considered embodiments is associated with the general power flow associated with the n-th motor. Each limit value of the n-th power flow Piim,n,prop and Piim,n,reg is defined as a polynomial with expression anTn2+bnTn+cn(thus, second-degree polynomial) wherein an, bn, cnare coefficients dependent on a rotational speed of the corresponding n-th electric motor, and Tnis a torque of the corresponding n-th electric motor (which may be a propulsion torque, associated with an index PROP, prop in the presently adopted references, or a regeneration torque REG, reg in the presently adopted references). The first overall reference limit value Piim,ioi PROP OL of the absorbed electric power flow comprises, in the preferred embodiments of the invention, a sum of each n-th limit absorbed power flow Piim,n,prop (Piim,TOT_PROp_oL = Piim,1,prop + Piim,2,prop + Plim,3,prop + Plim,4,prop the IHOSt general instance), in the same way as the second overall reference limit value Piim,ioiREG OL of the generated electric power flow comprises a sum of each n-th limit generated power flow Piim,n,reg(Piim,TOT_REG_OL = Piim,i,reg+ Piim,2,reg + Plim,3,reg + Plim,4,reg in the IHOSt general instance). The suffix "OL" as a subscript to the listed values refers to the determination in open loop of the reference values, i.e. based on a computational model - as in the case of the preferred embodiments of the invention - or of listed plans.

[0034] Once the values Piim,T0T_PR0P_0L and Piim,TOT_REG_OL are known, according to the teachings of document 102023000023517 mentioned in the foregoing (block OL), it is possible to calculate a first extreme reference value TnfPROpOL for the torque Tndelivered by each n-th electric motor as a function of the first overall limit value Piim,TOT PROP OL and of at least one boundary condition formulated as a function of the torque Tnof one or more of the electric motors (blocks m, TV) and a second extreme reference value Tn,REG OL for the torque Tnabsorbed by each n-th electric motor as a function of the second overall limit value Piim,TOTREG OL and of a boundary condition formulated as a function of the torque Tnof one or more of the electric motors (blocks m, TV). In total, therefore, there are calculated the values TL,PROP-OL, T2,PROP-OL, T3fRR0P_0L / T4fRRGp_OL and TifREG_OL / T2,REG_OL, T3fREGOLZ T4fREG 0L- Such values are extreme values, i.e. they are (absolute) maximum values in the respective operational domains (delivered torque and absorbed torque, respectively). If the values are considered as a function of their respective sign (which is positive for a delivered torque and negative for an absorbed torque), it may be observed that the values TifRROpOL, T2,PROP_OL, T3fRR0p_0L, T4fRR0p_0L correspond to maximum torque values, and the values TifREGon T2,REG OL, TsfREGon T^REG OL correspond to minimum torque values.

[0035] Generally speaking, examples of boundary conditions may include at least one between: a ratio m (block m) of a torque delivered and / or absorbed by a front axle FA to a torque delivered and / or absorbed by a rear axle RA of the motor vehicle V, a relationship (block TV) between a torque delivered and / or absorbed by a right wheel and by a left wheel of an axle FA or RA of the motor vehicle.

[0036] In the most general instance of a vehicle V with a powertrain comprising an electric motor for each of the wheels FL, FR, RL, RR, it is possible to express the value Rum,n,prop with the following expressions:

[0037] - Motor Ml: Piim,i,RR0P=ai,PROpTifpRop2+bifPROPTI,PROP+CI,PROP

[0038] - Motor M2: Pnm,2,PR0P=a2,PROpT2,pRop2+b2,pRopT2,pRop+C2,pRop

[0039] - Motor M3: Plim,3,PROP=33,PROPT3,PROP2+b3fPROpTs,PROp+C3fPROP

[0040] - Motor M4: Plim,4,PROP=a4,PROpT4,PROP2+b4fPROpT-J,PROp+C4fPROP and the value Piim,n,REG with the following expressions:

[0041] - Motor Ml: Plim,l,REG=Ul,REGTl,REG2+blfREGT1,REG+C1,REG

[0042] - Motor M2: Plim,2,REG=a2,REGT2,REG2+b2,REGT2,REG+C2,REG - Motor M3: Plim,3,REG=&3,REGT3,REG2+b3fREGTS,REG+C3,REG

[0043] - Motor M4: Plim,4,REG=a4,REGT4,REG2+b4fREGT4,REG+C4,REG

[0044] The coefficients ai, bi, Ci, a2, b2, C2, a3, b3, c3, a4, b4, C4 (either with index PROP, or with indexREG) are mapped as a function of the operation mode (PROP for the delivered torque,REG for the absorbed torque), of the rotational speed of each of the electric motors Ml, M2, M3, M4, and therefore the expression of the n-th electric power flow varies as a function of the rotational speed of the n-th motor. Each equation which describes the electric power flow Film,TOT,PROP-OL or Piim,TOT,REG_OL is an equation with four variables T4, T2, T3, T4(either with index PROP, or with indexREG) which may be solved if combined into a system with three further equations, corresponding to the boundary conditions mentioned in the foregoing. Such equations comprise:

[0045] - a first difference 2ATVR(2A) between the second torque T2delivered (or absorbed) by the second motor M2 to (or from) the rear right wheel RR and the first torque Ti delivered (or absorbed) by the first motor Ml to (or from) the rear left wheel RL. The difference may have different values as a function of the use as a boundary condition for calculating Pnm,TOT,PROP OL or as a boundary condition for calculating Pnm,TOT,REGOL,'

[0046] - a second difference 2ATVF(2B) between the fourth torque T4delivered (or absorbed) by the fourth motor M4 to (or from) the front right wheel ER and the third torque T3delivered (or absorbed) by the third motor M3 to (or from) the front left wheel FL. As stated in the foregoing, the difference may have a different value as a function of the use as a boundary condition for calculating Pnm,TOT,PROP OL or as a boundary condition for calculating Piim,TOT,REG_OL;

[0047] In other words, these two relationships are representative of a condition of active asymmetrical torque distribution between the wheels of the rear axle RA and of the front axle FA (torque vectoring - the coefficient 2 is a mere convention, deriving from the fact that the amount ATVR, ATVFrepresents the torque which is subtracted from a wheel and transferred to the other, and thus the global difference amounts to 2ATV)

[0048] T2- Ti = 2ATVR

[0049] T4- T3= 2ATVF - a ratio m of a sum of the fourth torque T4 and of the third torque T3, delivered (or absorbed) by the motors M4, M3 to (or from) respective wheels of the front axle FA, to a sum of the torque T2 and of the torque Ti delivered (or absorbed) by the motors M2, Ml to (or from) the respective wheels of the rear axle RA, therefore

[0050] (3) m = (T4+T3) / (T2+TJ

[0051] Thus, m expresses a torque distribution ratio between the front axle and the rear axle. As stated in the foregoing, the difference may have a different value as a function of the use thereof as a boundary condition for calculating Pnm,TOT,PROP OL or as a boundary condition for calculating Piim,TOT,REG_OL;

[0052] The amount Pnm,T0T (either with indexPROp, or with index REG) describes a four-dimensional geometric locus (dimensions Tp, T2, T3fT4) which cannot be represented graphically but which is completely defined in itself. In the same way, the expressions of the boundary conditions describe geometric loci in the same fourdimensional space, the common intersection whereof with the geometric locus Pnm,TOT yields a locus having coordinates (T^PROP-OL, T2,PROP-OL, TS^ROP^L, T4fPRop_oL) or (Tt'REG-OL, T2,REG_OL / T3fREG_oL / T4fREG_OL) which correspond to the maximum or minimum torques (considered with their sign) which can be delivered or absorbed by the electric motors Ml, M2, M3, M4 at the rotational speeds at a given instant, and as a function of the power limit envisaged for the instantaneous operating condition.

[0053] In other words, the geometric loci Pnm,TOT,PROP OL and Piim,TOT,REG OL are isopower loci (maximum and minimum power, considered while keeping the sign) whereon the locus of coordinates (T^RROR-OL, T2,PROP-OL, T3fPRop_oL / T4fPRop_oL) or (Ti'KEG-OL, T2,REG_OL / T3rREG_OLr T4rREG_OL) shall be located in order to simultaneously meet the conditions of torque distribution within the powertrain and the condition of the limit value of the overall power flow in the powertrain. Moreover, in this way it is possible to define a first overall extreme reference value of the delivered torque (also named first overall target or barycentric torque) - which is determined in open loop — TTOT,PROP_OL=Ti'EROR-OL, T2,PROP_OL, T3,PROP—OL / T4fpRop_oL and a second overall extreme reference value of the absorbed torque (also named second overall target or barycentric torque) - which is determined in open loop TTOT,REG OL = T1,REG—OL, T2,REG—OL, T3fREG_OL, T4fREG_OL•

[0054] According to the invention, the first torque correction TCL,PROP and the second torque correction TCL,REG are formulated in terms of barycentric correction (i.e., corrections of target values), therefore as corrections of the target torques determined in open loop TTOT,PROP OL, TROT,REG OL, which are subsequently distributed to the individual motors on the basis of the ratio m. In this regard, it will be observed that the torque distribution asymmetries between the left side and the right side ATVFand ATVR are not involved in the determination of the corrections TCL,PROP and TCL,REG: such asymmetries are values which are determined in open loop (therefore according to a model-based calculation or by means of a map, which are not changed by corrections in open loop, nor do they appear in the expression of the barycentric torque due to self-elimination at the moment of the sum. For the definition of ATVFand ATVR, they appear in association with the torques developed on the left side of the vehicle, exhibiting an opposite sign and an identical absolute value with respect to the sign and the absolute value exhibited in association with the torques developed on the right side of the vehicle. The corrections may be applied only on the basis of the torque distribution ratio between the front axle FA and the rear axle RA.

[0055] As can be seen in the diagram of Figure 1, the torques TTOT,PROP OL, TTOT,REG OL are only one item of data among the data input into the block CL. In other words, the corrections TpROpCL and TREG CL are determined as a function of: the first overall extreme reference value

[0056] (TROT,PROP OL) comprising a sum of the first extreme reference values (TifpRop_oL, T2,PROP_OL,‘ T3fpRop_oL, T4fpRop_oL) of the torque Tnof each n-th electric motor, the second overall extreme reference value

[0057] (TROT,REG OL) comprising a sum of the second extreme reference values (TifREG_oL, T2,REG_OL,‘ T3fREG_oL, T4fREG_oL) of the torque Tnof each n-th electric motor, the first overall reference limit value

[0058] (Film,TOT PROP) of an electric power flow of the powertrain and said second overall reference limit value (Pnm,TOTREG) of an electric power flow of the powertrain,

[0059] - a target propulsion torque (TTGTPROP),

[0060] - a target regeneration torque (TTGT REG),

[0061] - an overall torque delivery limit of the one or more electric motors TTOT,LIM_MOT_PROP (the sum of Tlf LIM-MOT_PROP,

[0062] T2,LIM-MOT-PROP, T3,LIM_MOT_PROPZ T4fLIM_MOT_PROP)r

[0063] - an overall torque absorption limit of the one or more electric motors TTOT,LIM_MOT_REG (the sum of Tlf LIM-MOT_REG, T2,LIM-MOT_REGZ T3,LIM_MOT_REG,‘ T4,LIM_MOT_REG)r

[0064] - an overall limit grip torque of the vehicle in the propulsion mode,

[0065] - an overall limit grip torque of the vehicle in the regeneration mode.

[0066] Preferably, the grip limits used in the determinations made by the method according to the invention comprise torque limit values calculated by means of traction control algorithms (block TTCS), and in particular they include limit grip torques in the propulsion mode Ti,TCS_PROP_OL / T2,TCS_PROP_OL / T3,RCS_ PROP-OL, T4,TCS PROP OL and limit grip torques in the regeneration mode TifTCS-REG-OL, T2,TCS_REG_OL / T3,TCS-REG-OL, T4,TCS_REG_OL•

[0067] It is therefore possible to define a domain of limit torques Tn,MOT_PROP (Tl,MOT-PROP / T2,MOT-PROP / T3,MOT-PROP / T4,MOT-PROP) deliverable by the electric motors Ml, M2, M3, M4

[0068] (maximum torques, considering the sign thereof), as well as a domain of the torques Tn,MoiREG (TI,MOT REG / T2,MOT REG / T3,MOT REG; T4,MOT REG) absorbable by the electric motors Ml, M2, M3, M4 (maximum torques, considering the sign thereof) : they are defined by the intersection between the operational limits of the electric motors and the requested torque distribution, thus: propulsion (delivered torques)

[0069] TROT,MOT_PROP=T1,MOT_PROP + T2,MOT-PROP + T3,MOT-PROP + T4,MOT_PROP Tl,MOT_PROP — TifLIM—MOT—PROP T2,MOT_PROP — T2,LIM_MOT_PROP T3,MOT_PROP — T3,LIM-MOT-PROP T4,MOT_PROP — T4,LIM_MOT_PROP

[0070] T4,MOT_PROP - T3,LIM—PROP=2ATVR T2,MOT_PROP—11,LIM—PROP=2ATVR ft!=(T4fMOT_PROP + T3,MOT_PROP) / (T2,MOT_PROP + Ti,MOT_PROp) regeneration (absorbed torques)

[0071] TTOT,MOT_REG—T1,MOT_REG + T2,MOT_REG + T3,MOT_REG + T4,MOT_REG

[0072] Tl,MOT_REG — Tl,LIM—MOT—REG

[0073] T2,MOT_REG — T2,LIM_MOT_REG

[0074] T3,MOT_REG — T3,LIM_MOT_REG

[0075] T4,MOT_REG — T4,LIM_MOT_REG

[0076] T4,MOT_REG - T3,LIM_REG=2ATVR

[0077] T2,MOT_REG—T1,LIM_REG=2ATVR m=(T4,MOT-REG + T3,MOT-REG) / (T2,MOT_REG + TI,M0T_REG)

[0078] Once the torques TTGT,PROP (barycentric / target propulsion torque), TROT,PROP OL, TTCS,PROP OL, TTOT,MOT PROP are known, it is possible to define the correction TPROpCL according to the diagram shown in Figure 2. The correction TPROpCL is determined on the basis of the difference between the limit torque Pnm,TOT PROP OL and an overall electric power PACT,PROP absorbed by the motors Ml, M2, M3, M4 by using a proportional-integral control PI. The values of the correction TPR0R CL have an inferior saturation limit L, ISPROp which equals the opposite of the torque TROT,PROP OL (thus, ISPRQP=—TROT,PROP OL / la this way it is possible to avoid in every case the generation, by the control in closed loop, of a sign reversal of the value TPROpCL + TTOT,PROP OL), and a superior saturation limit (H, SSPROp) defined by subsequent selections and combination. In detail, the superior saturation limit is defined by extracting the minimum value (block MINI) between the values of the torques TTOT,MOT PROP and TTCS,PROP OL- The purpose of the operation is avoiding exceeding the torque limits (TTOT,MOT PROP) or the grip limits (TTCS,PROP OL) of the vehicles. If the torque availability is lower than the value which would lead to grip loss, then the torque availability becomes the limit, so as to avoid excessive thermal and mechanical stresses. If, on the contrary, a condition is present wherein the torque limit which generates grip loss is reached before the saturation of the available torque, then the condition of grip loss becomes the limit, because it is not generally acceptable to operate outside the grip limits.

[0079] The torque value TTOT,PROP OL, determined in open loop, is subtracted from the value extracted by the operator MIN and from the barycentric torque value TTGT(blocks DI, D2). The lower result of the differences calculated at the blocks DI and D2 is extracted by a second minimum operator (block MIN2) and becomes the upper saturation limit SSPROP. The difference DI represents the difference between the barycentric torque TTGTfRROp and the torque TTOT,PROP OL (maximum torque, considering the sign) determined in open loop, and therefore represents the torque difference which is necessary to meet the torque target TTGTfRROp when the absorbed electric power is lower than the limit of the electric motors. The difference D2 represents the difference between the torque TTOT,PROP OL and the lower torque between the maximum available barycentric propulsion torque TTOT,MOT PROP and the maximum barycentric torque admissible before generating grip loss TTCS,PROPOL- Substantially, D2 represents the torque difference corresponding to the maximum increase which is possible taking into account the delivery limit of the electric motors or the grip limit of the vehicle. Similarly to what has been described in the foregoing, the superior saturation limit takes into account the most stringent condition, so as to avoid operating in critical conditions on either side.

[0080] Figure 3 and Figure 4 exemplify the control action in closed loop with the electric motors operating in the propulsion mode. In figure 3, the double diagram shows the evolution in time of the electric power and of the barycentric torque correction TRROPCL-

[0081] Before the time instant A the electric power PACT,PROP absorbed by the electric motors is lower than the limit value Piim,TOT PROP: the control in closed loop is not applying any correction. At the instant A the electric power PACT,PROP absorbed by the electric motors exceeds the limit value Pnm,TOT PROP: the control in closed loop applies a torque correction TRROpCL- At the instant B, following the instant A, the electric power PACT,PROP absorbed by the electric motors becomes identical to the limit value Piim,TOT PROP due to the correction TRROpCL: the control in closed loop keeps the correction constant, so as to maintain the condition achieved.

[0082] Referring to Figure 4, it shows time diagrams of the electric power absorbed by the motors, of a speed Vsof the vehicle, of the barycentric torques and of the torque correction.

[0083] Before the time instant A, the barycentric torque TTGT,PROP is lower than the torque TTOT,PROP OL and the electric power PACT,PROP absorbed by the electric motors is lower than the limit value Pnm,TOT PROP: the control in closed loop does not apply any correction.

[0084] At the time instant A the barycentric torque TTGTexceeds the torque TTOT,PROP OL due to a manoeuvre of the driver, but the electric power PACT,PROP absorbed by the electric motors remains lower than the limit value Piim,TOT PROP: the control in closed loop applies a correction TPROpCL which increases with positive sign, so as to meet the request of barycentric torque TTGTfPROp as much as possible.

[0085] At the time instant B, the correction TPR0PCL stops increasing, due to reaching the superior saturation limit SSPR0P. The torque resulting from the controls in open loop and in closed loop TTOT,PROP OL + TPR0PCL is limited to the minimum value between TTCS,PROP OL and TTOT,MOT PROP- The absorbed electric power PACT,PROP increases at a lower rate with respect to the time interval preceding the instant B (between A and B).

[0086] At the time instant C, the electric power PACT,PROP absorbed by the electric motors equals the limit Piim,TOT PROP: the correction TPROpCL starts being decreased.

[0087] As regards the operation in the regeneration mode, once the torques TTGTfREG(barycentric / target regeneration torque), TROT,REG OL, TRCS,REG OL, TROT,MOT REG are known, it is possible to define the correction TREG CLaccording to the diagram shown in Figure 5.

[0088] The correction TREG CLis determined based on the difference between the limit power Piim,ioiREG OL and an overall electric power PACT,REG generated by the motors Ml, M2, M3, M4 by using a proportional-integral control PI. The values of the correction TREG CL have a superior saturation limit (H, SSREG) which equals the opposite of the torque TTOT,REG_OL (thus, ISRR0R= -TTOT,REG_OL; this enables preventing, in any case, the control in closed loop from generating a sign reversal of the amount TREG CL+ TROT,REG OL) and an inferior saturation limit (L, ISREG) defined by subsequent selections and combinations. In more detail, the inferior saturation value is defined by extracting the maximum value (block MAXI) between the values of the torques TTOT,MOT REG and TTCS,REGOL- The purpose of the operation consists in avoiding exceeding the regeneration (TTOR,MOT_REG) or the grip (TTCS,REG_OL) torque limits of the vehicle. The maximum operator MAXI, instead of a minimum operator as in the case of the propulsion mode, is due to the fact that, in the regeneration mode, the torques have a negative value, and therefore the maximum operator practically extracts the torque having the lowest absolute value.

[0089] If a condition is present wherein the capacity of torque absorption TTOT,MOT REG by the electric motors has an absolute value which is lower - i.e., higher, considering the sign - than the value which would lead to grip loss, then the capacity of torque absorption TROT,MOT REG becomes the limit, so as to avoid grip loss. If, on the contrary, a condition is present wherein a limit of absorbed torque is achieved beyond which a grip loss is generated before saturating the torque absorbable by the electric motors (i.e., the second has an absolute value higher than the first but, due to the sign, is lower than the first), then the condition of grip loss becomes the limit.

[0090] The torque value TTOR,REG OL determined in open loop is subtracted from the value extracted by the operator MAXI and from the barycentric regeneration torque value TTGT,REG (blocks D3, D4). The highest result of the differences operated at the blocks D3 and D4 is extracted by a second maximum operator (block MAX2) and becomes the inferior saturation limit ISREG. The difference D3 represents the difference between the barycentric regeneration torque TTGT,REG and the torque TTOT,REG OL (a minimum torque, considering the sign) which is determined in open loop, and therefore it represents the torque difference which is necessary to meet the target regeneration torque TTGT,REG when the generated electric power has an absolute value lower than the limit of the electric motors (i.e. a higher value, considering the sign). The difference D4 represents the difference between the regeneration torque TTOT,REG OL and the higher (considering the sign, therefore the lower in absolute value) between the maximum available barycentric regeneration torque TTOT,MOT REG and the maximum barycentric torque admissible before generating grip loss TTCS,REGOL- Such torque difference corresponds to the maximum possible decrease (considering the sign) taking into account the delivery limit of the electric motors or the grip limit of the vehicle.

[0091] Similarly to what has been described in the foregoing, the inferior saturation limit takes into account the most stringent condition, in such a way as to avoid operating in critical conditions from either point of view.

[0092] Figure 6 and Figure 7 exemplify the action of the control in closed loop with the electric motors operating in the regeneration mode. In Figure 3, the double diagram shows the evolution in time of the electric power and of the barycentric torque correction TPROPCL-

[0093] Before the time instant A, the electric power PACT,REG generated by the electric motors is higher (considering the sign, but the absolute value thereof is lower) than the limit value Piim,ioiREG: the control in closed loop does not apply any correction. At the instant A, the electric power PACT,REG generated by the electric motors exceeds (in absolute value, but it is lower considering the sign!) the limit value Pnm,TOTREG: the control in closed loop applies a torque correction TREG CL- At the instant B, following instant A, the electric power PACT,REG absorbed by the electric motors becomes identical to the limit value Pnm,TOTREG due to the correction TREG CL: the control in closed loop keeps the correction constant, thereby maintaining the achieved condition.

[0094] With reference to Figure 7, it shows time diagrams of the electric power generated by the motors, of the vehicle speed Vs, of the barycentric torques and of the torque correction.

[0095] Before the time instant A, the barycentric torque TTGT,REG is higher (considering the sign, but it is lower in absolute value) than the torque TTOT,REG OL, and the electric power PACT,REG generated by the electric motors is higher (considering the sign, but it is lower in absolute value) than the limit value Pnm,TOTREG: the control in closed loop does not apply any correction.

[0096] At the time instant A, the barycentric torque TTGTfREGexceeds the torque TTOT,REG OL due to a manoeuvre of the driver, but the electric power PACT,REG delivered by the electric motors is still higher (considering the sign, but it is lower in absolute value) than the limit value Piim,TOTREG: the control in closed loop applies a correction TREG GL which decreases with negative sign (increases in absolute value) so as to satisfy the request of barycentric torque TTGTfREGas much as possible.

[0097] At the time instant B, the correction TREG CLstops decreasing (increasing in absolute value) due to reaching the inferior saturation limit ISREG. The torque resulting from the controls in open loop and in closed loop TTOT,REG OL + TREGCL is limited to the maximum value (the minimum absolute value) between TTCS,REG OL and TROT,MOT REG- The generated electric power PACT,REG decreases (increases in absolute value) at a lower rate with respect to the time interval preceding the instant B (between A and B).

[0098] At the time instant C, the electric power PACT,REG generated by the electric motors equals the limit Piim,TOTREG: the correction TREG CL starts being decreased (in absolute value, but increased considering the sign).

[0099] The corrections TPROpCL and TREG CL shall therefore be distributed to the electric motors while respecting the envisaged torque distribution m. As stated in the foregoing, this does not include the boundary conditions relating to the torque asymmetry between the right side and the left side, as they are not subjected to correction because they are neutralized in the barycentric torques on which the computation is based, and in any case they are already ensured by the calculation in open loop.

[0100] The values of torque correction for the electric motors, therefore, correspond to the solution of the following systems of equations.

[0101] Propulsion

[0102] I) TpRQP_CL=En(Tn,PPOP-CL)=TifpRQP_CL + T2,PROP_CL + T3fpRQP_CL +

[0103] T4,PROP CL (first and second correction fraction)

[0104] II) T2,PROP_CL=TifpR0P_CL

[0105] III) T4fpR0P_CL=T3fpR0P_CL iv) m = (T4fpR0P_CL + T3fpR0P_CL) / (T2,PROP_CL + TifpR0P_CL) wherein TnfPROpCL is the correction to be applied to the n-th motor in the propulsion mode, by summing it, while keeping the sign, to the value TnfPROpOL- From 11) and ill) it is possible to infer that, in the first and in the second correction fraction, a torque correction on a right side of the vehicle and a torque correction on a left side of the vehicle have identical value.

[0106] Regeneration

[0107] 1) TREG-GL = En(Tn,REG_CL)=TifREG-GL + T2,REG_CL + T3fREG-GE+

[0108] T4,REG CL (third and fourth correction fraction) ii) T2,REG_CL=T1r REG_CL

[0109] 111) T4r REG_CL=T3r REG_CL iv) m = (T4fREG-GL+ T3fREG-GL) / (T2,REG_CL + TifREG-GL) wherein Tn,REG CL is the correction to be applied to the n-th motor in the regeneration mode, by summing it, while keeping the sign, to the value Tn,REG OL, wherein TnfRR0RCL is the correction to be applied to the n-th motor in the propulsion mode, by summing it, while keeping the sign, to the value TnfRR0ROL- From 11) and ill) it is possible to infer that, in the third and in the fourth correction fraction, a torque correction on a right side of the vehicle and a torque correction on a left side of the vehicle have identical value.

[0110] Thanks to the method according to the invention it is possible to increase the safety of the battery both in the propulsion mode and in the regeneration mode, by correcting the torque in such a way as to avoid exceeding the power limits for a prolonged time. Moreover, the driver's satisfaction is ensured when the torque is available in the system and the battery limits are not completely saturated, while meeting the predetermined torque distribution. In the regeneration mode, it is possible to take the maximum advantage of the electric motors in order to decelerate the vehicle in the stead of the mechanical brakes, when the braking torque is available and the battery limits are not completely saturated, while meeting the predetermined torque distribution.

[0111] Of course, the implementation details and the embodiments may amply vary from what has been described and illustrated, without departing from the extent of the present invention, as defined by the annexed claims.

Claims

CLAIMS1. A method for controlling a torque of one or more electric motors (Ml; M2; M3; M4) of an electric powertrain of a vehicle (V), the method including:- defining, for each n-th electric motor (Ml; M2; M3; M4), a first reference limit value (Plim,n,prop) of a n-th flow of electric power absorbed by the n-th electric motor, and defining, for each n-th electric motor (Ml; M2; M3; M4), a second reference limit value(Plim,n,reg) of a n-th flow of electric power generated by the n-th electric motor,- defining a first overall reference limit value (Plim,TOT_PROP) of the absorbed electric power flow comprising a sum of each n-th limit value of absorbed power (Plim,n,prop), and defining a second overall reference limit value (Plim,TOT_REG) of the generated electric power flow comprising a sum of each n-th limit value of generated power (Plim,n,reg),- defining (OL) a first reference extreme value (Tn,PROP_OL) for a torque Tn delivered by each n-th electric motor as a function of said first overall limit value (Plim,TOT_PROP) of the absorbed electric power flow and a boundary condition formulated as a function of the torque Tn of one or more of the electric motors (m, TV), and defining a second extreme reference value (Tn,REG_OL) for the torque Tn absorbed by each n-th electric motor as a function of said second overall limit value (Plim,TOT_REG) of the generated electric power flow and a boundary condition formulated as a function of the torque Tn of one or more of the electric motors (m, TV), determining (CL) a first torque correction (TPROP_CL) to be applied to the one or more first extreme reference values (Tn,PROP_OL) of the torque Tn deliveredby each n-th electric motor, and calculating a second torque correction (TREG_CL) to be applied to the one or more second extreme reference values (Tn,REG_OL) of the torque Tn absorbed by each n-th electric motor, splitting (mCL) the first torque correction (TCL,PROP) into a first correction fraction (T3,PROP_CL; T4,PROP_CL) associated with the front axle (FA) of the vehicle and a second correction fraction (T1,PROP_CL; T2,PROP_CL) associated with a rear axle (RA) of the vehicle (V) as a function of a first target torque split ratio (mPROP), and splitting said second torque correction (TCL,REG) into a third correction fraction (T3,REG_CL; T4,REG_CL) associated with the front axle (FA) of the vehicle, and a fourth correction fraction (T1,REG_CL; T2,REG_CL) associated with the rear axle (RA) of the vehicle according to a second target torque split ratio (mREG), applying the first correction fraction (T3,PROP_CL; T4,PROP_CL) to the set of first extreme reference values (T3,PROP_OL, T4,PROP_OL) of the torque delivered to the front axle (FA) by one or more corresponding electric motors (M4, M3), applying the second correction fraction(T1,PROP_CL; T2,PROP_CL) to the set of the first extreme reference values (T1,PROP_OL, T2,PROP_OL) of the torque delivered to the rear axle (RA) by one or more corresponding electric motors (Ml, M2), applying the third correction fraction(T3,REG_CL; T4,REG_CL) to the set of the second extreme reference values (T3,REG_OL, T4,REG_OL) of the torque absorbed from the front axle (FA) by one or more corresponding electric motors (M3, M4), and applying the fourth correction fraction (T1,REG_CL; T2,REG_CL) to the set of the second extreme reference values (T1,REG_OL, T2,REG_OL) of the torqueabsorbed from the rear axle (RA) by one or more corresponding electric motors (Ml, M2).

2. The method according to claim 1, wherein said first torque correction (TCL,PROP) and second torque correction (TCL,REG) are determined as a function of: a first overall reference extreme value (TTOT,PROP_OL) comprising a sum of the first reference extreme values (T1,PROP_OL, T2,PROP_OL; T3,PROP_OL, T4,PROP_OL) of the torque Tn of each n-th electric motor, a second overall extreme reference value (TTOT,REG_OL) comprising a sum of the second extreme reference values (T1,REG_OL, T2,REG_OL; T3,REG_OL, T4,REG_OL) of the torque Tn of each n-th electric motor, said first overall reference limit value (Plim,TOT_PROP) of absorbed electric power flow and said second overall reference limit value (Plim,TOT_REG) of generated electric power flow,- a target propulsion torque (TTGT_PROP)- a target regeneration torque (TTGT_REG)- an overall torque delivery limit of the one or more electric motors (Tl,LIM_MOT_PROP; T2,LIM_MOT_PROP; T3,LIM_MOT_PROP; T4,LIM_MOT_PROP),- an overall torque absorption limit of the one or more electric motors (Tl,LIM_MOT_REG, T2,LIM_MOT_REG, T3,LIM_MOT_REG; T4,LIM_MOT_REG),- a limit overall vehicle grip torque in propulsion (Tl,_TCS_PROP_OL, T2,_TCS_PROP_OL, T3,_TCS_PROP_OL; T4,_TCS_PROP_OL) a limit overall vehicle grip torque in regeneration (Tl,_TCS_REG_OL, T2,_TCS_REG_OL,T3,_TCS_REG_OL; T4,_TCS_REG_OL).

3. The method according to claim 1 or claim 2, including:- defining the first reference limit value of the n-th electric power flow as a respective polynomial withexpression an,PROPTn, PROP2+bn,PROPTn,PROP+cn,PROP wherein an,PROP, bn,PROP, cn,PROP are coefficients dependent on a rotational speed of the n-th electric motor, and Tn,PROP is a torque delivered by the n-th electric motor, and- defining the second reference limit value of the n-th electric power flow as a respective polynomial with expression an,REGTn,REG2+bn,REGTn,REG+cn,REG where an,REG, bn,REG, cn,REG are coefficients dependent on a rotational speed of the n-th electric motor, and Tn,REG is a torque absorbed by the n-th electric motor.

4. The method according to claim 3, comprising calculating said first extreme reference value for the torque Tn of each n-th electric motor by intersection between a geometric locus corresponding to said first overall limit value of the absorbed electric power flow (Plim,TOT_PROP) and one or more geometric locus representative, each, of a boundary condition formulated as a function of the torque Tn of one or more of the electric motors.

5. The method according to any one of claims 2 to 4, wherein said first torque correction (TCL,PROP) is determined on the basis of a difference between said first overall limit value of the absorbed electric power flow (Plim,TOT_PROP) and an electric power flow (PACT,PROP) absorbed by the one or more electric motors (Ml, M2, M3, M4) and comprising an inferior saturation limit (ISPROP) and a superior saturation limit (SSPROP), wherein:- said inferior saturation limit (ISPROP) comprises the opposite of said first overall extreme reference value (TTOT,PROP_OL),- said superior saturation limit (SSPROP) comprises the minimum value between a first difference (DI) and a second difference (D2), the first difference being adifference between said target propulsion torque (TTGT_PROP) and said first overall extreme reference value (TTOT,PROP_OL), the second difference being a difference between the minimum of said overall torque absorption limit of the one or more electric motors (Tl,LIM_MOT_PROP, T2 ,LIM_MOT_PROP, T3,LIM_MOT_PROP; T4,LIM_MOT_PROP) and said limit overall vehicle grip torque in propulsion (Tl,_TCS_PROP_OL, T2,_TCS_PROP_OL, T3,_TCS_PROP_OL; T4,_TCS_PROP_OL), and said and said first overall extreme reference value (TTOT,PROP_OL).

6. The method according to any one of claims 2 to 5, wherein said second torque correction (TCL,REG) is determined on the basis of a difference between said second overall extreme value of the generated electric power flow (Plim,TOT_REG) and an electric power flow (PACT,REG) generated by the one or more electric motors (Ml, M2, M3, M4) and comprising an inferior saturation limit (ISREG) and a superior saturation limit (SSREG), wherein:- said superior saturation limit (SSREG) comprises the opposite of said second overall extreme reference value (TTOT,REG_OL),- said inferior saturation limit (ISREG) comprises the maximum value between a third difference (D3) and a second difference (D4), the third difference being a difference between said regeneration target torque (TTGT_REG) and said second overall extreme reference value (TTOT,REG_OL), the fourth difference being a difference between the maximum of said overall torque absorption limit of one or more electric motors (Tl,LIM_MOT_REG, T2,LIM_MOT_REG, T3,LIM_MOT_REG; T4,LIM_MOT_REG) and said limit overall vehicle grip torque in regeneration (Tl,_TCS_REG_OL, T2,_TCS_REG_OL, T3,_TCS_REG_OL; T4,_TCS_REG_OL), and said second overall extreme reference value (TTOT,REG_OL).

7. The method according to any of the preceding claims, wherein in each of said first, second, third and fourth correction fractions a torque correction on a right side of the vehicle and a torque correction on a left side of the vehicle have identical value.

8. The method according to any one of the preceding claims, comprising calculating said second extreme reference value for the torque Tn of each n-th electric motor by intersection between a geometric locus corresponding to said overall limit value of the generated electric power flow (Plim,TOT_REG) and one or more geometric locus representative, each, of a boundary condition formulated as a function of the torque Tn of one or more of the electric motors.

9. The method according to any of the preceding claims, wherein said one or more boundary conditions comprise at least one of:- a relationship between a torque delivered, or absorbed, by one or more of said electric motors to, or from, a front axle (FA) and a torque delivered, or absorbed, by one or more of said electric motors to, or from, a rear axle of the vehicle (RA),- a relationship between a torque delivered, or absorbed, by a first electric motor to, or from, a right wheel of a vehicle axle, and a torque delivered, or absorbed, by a second electric motor to, or from, a left wheel of the same vehicle axle.

10. The method according to claim 9, wherein the motor vehicle comprises a first electric motor (Ml) operatively associated with a left rear wheel (RL), a second electric motor (M2) operatively associated with a right rear wheel (RR), and a third electric motor (M3) operatively associated with a front axle (FA).

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